Communication systems support the provisioning of voice, data, multimedia or other services and information to subscribers. A problem with prior communication systems is that a particular subscriber may pirate the services of another subscriber in the system without properly subscribing for the services. One solution to this problem is to assign a unique user name and password to the subscribers and to restrict access to particular services based upon a successful response to a query for a subscriber's user name and password. This solution is ineffective, however, when one subscriber assumes the identity of another subscriber by misappropriating the user name and password of the other subscriber and, thereby, obtains access to the other subscriber's services.